The reaction of phenol or bisphenols with dialkyl carbonates is slow leading to long reaction times even when catalyzed by various Lewis acids. Many catalysts including various titanates and stannates have been described for use in the above mentioned reaction. Examples may be found in U.S. Pat. Nos. 4,252,737; 4,182,726; 4,552,704; as well as German laid open applications DE Nos. 2,736,063 and 2,736,062.
Somewhat faster transesterification reaction rates are obtained by the utilization of phenyl acyl esters or bisphenyl acyl diesters. Examples of the foregoing may be found in U.S. Pat. Nos. 4,182,726 and 4,452,968. The teachings of all of the foregoing United States Patents are incorporated herein by reference thereto.
In U.S. Pat. No. 4,452,968 an integrated process for the preparation of aromatic polycarbonates was disclosed wherein the methyl acetate by-product formed in the transesterification of a bisphenol diacetate with a dialkyl carbonate was recycled by heating the alkyl ester to form a ketene and subsequently such ketene was reconverted by reaction with a bisphenol to form additional quantities of the bisphenol diacetate. For the teachings contained therein the above identified patent is incorporated herein by reference thereto.
However the preparation of a ketene intermediate involves high temperatures, and does not attain efficiences of operation sufficient to permit successful commercialization of such an integrated process as is disclosed in U.S. Pat. No. 4,452,968.
It would be desirable if there were provided a process for preparation of aromatic carbonates, including methyl aryl carbonates, arylene bis (methyl carbonates and aromatic polycarbonates that allows for ease of conversion of phenol and bisphenol reactants, and high efficiency in the regeneration of the derivatizing agent.